Electrodes of the type discussed in the above referenced patent and patent applications are well known for use in the art of providing light at small wavelengths, e.g., UV and DUV, i.e., below about 500 nm, using halogen based gas discharge media within an enclosed chamber and providing the gas discharge between a pair of electrodes at very high voltages, e.g., tens of thousands of volts and high amperage, e.g., hundreds of amps, in very short duration electrical discharges in the medium, e.g., tens of nanoseconds. This pulsed laser light is used for a variety of industrial purposes, e.g., in integrated circuit photolithography to expose photoresist on wafers by passing the light through a mask (reticle) to accomplish the desired exposure. The stability of various parameters of the light delivered to the wafer as provided by the laser light source is critical to proper performance of the manufacturing process, e.g., the proper exposure of the photoresist to define microscopic patterns on the wafer for manufacturing integrated circuits with critical dimensions measured in under 0.1 microns.
One aspect of this criticality of the maintenance of the stability of the light delivered is the maintenance of the stability, pulse-to-pulse and over long periods of operation, measured in tens of billions of pulses, of the electrodes. The above referenced patent and patent applications discuss various aspects of the geometries, materials and the like utilized for such electrodes. Applicants have developed aspects of electrode materials and geometries and structures aimed at increasing the discharge stability pulse to pulse and over life and at increasing useful life during which such stable pulses can continue to be provided in order to improve the efficiency and economic of operating such laser light source systems as will be explained in more detail below.
Applicants have noticed an end wear region of the discharge receiving region of electrodes generally just beyond where the electrodes being used by applicant' assignee in laser systems begin a roll-off toward an end portion of the electrodes, wherein, e.g., the erosion causes the discharge to widen somewhat at the end which hastens end of life for the electrode. Applicants herein propose certain aspects of embodiments of the present invention that will alleviate this end of life syndrome for electrodes.